This invention relates generally to control systems for locking an automatic shift lever in PARK position unless the ignition is in RUN position and the service brake is applied, and, more particularly, to such a system in which the ignition key cannot be removed unless the shift lever is in PARK position.
Many systems have been devised to lock a vehicle's automatic transmission shifter in PARK position unless and until the vehicle's service brake is applied. This is a safety device that assures that the vehicle cannot be inadvertently placed in motion. These are referred to as BTSI (Brake-Transmission Shifter Interlock) systems. BTSI systems usually provide a latch which is automatically operated, via spring bias or cam means, upon movement of the shifter to PARK position, to block operation of the shifter detent, thus blocking shifter movement. Closure of the brake switch by applying the brakes operates a solenoid to retract or disable this latch and enable movement of the lever out of PARK to an operating position. Such a system is shown in U.S. Pat. No. 5,062,509--Carpenter.
Many other systems have been devised which prevent movement of the vehicle ignition key to OFF position for removal unless the vehicle's automatic transmission shifter is in PARK position and locks the shifter in PARK until the key is inserted and moved to RUN position. Some vehicles utilize this shifter-ignition interlock system in combination with a BTSI system. Such a combination is illustrated in FIG. 1 of the drawings which illustrates a system developed by General Motors Corporation (GM). This system is used in a vehicle having an ignition moveable among OFF, ACCESSORY, RUN and CRANK positions, a brake pedal movable between APPLIED and RELEASED positions, and a transmission control lever movable among PARK and a plurality of RUN positions.
FIG. 1 illustrates a combination BTSI and shift lever/ignition lock system 10 which includes a controller 12, termed a "PZM" by GM, which includes a microprocessor. Controller 12 responds to signals supplied to an input 14 to provide outputs 16 and 18 to control operation of a bistable ignition lock solenoid 20, having an armature 22, and outputs 24 and 26 of bi-stable shift lever pushbutton solenoid 28, having an armature 30.
Solenoid 20 responds to controller outputs 16 and 18 to extend and retract armature 22. When extended, armature 22 blocks movement of an ignition key (described later with respect to the invention) to OFF position, thus preventing key removal from its ignition lock cylinder. Similarly, solenoid 28 responds to controller outputs 24 and 26 to retract and extend armature 30. When extended, armature 30 engages a locking notch 32 of a pushbutton 34 which is carried by the usual automatic transmission shift lever (not shown) to operate a detente rod which cooperates with a detente plate to locate the lever in PARK and other positions, as shown in the aforementioned Carpenter patent.
A control circuit 36 provides "high" and "low" signals to input 14 of controller 12. When a low signal is provided, controller 12 activates outputs 18 and 26 to retract armature 22 and extend armature 30. This unblocks ignition key movement to OFF, enabling removal, and locks pushbutton 34, which locks the vehicle transmission in PARK.
Circuit 36 includes a power source 38, such as the vehicle battery, and the vehicle ignition 40 which includes first and second switches 42 and 44 that are located in parallel branch circuits. Ignition switch 44 is connected in series with a pushbutton control switch 46 that is normally open and is closed by a follower 48 operated by cam surface 50 on shift lever pushbutton 34. Switch 42 connects with controller input 14 by conductor 52.
Ignition switch 42 connects to a BTSI solenoid 54 through a control switch 56, which is closed when the shift lever is in PARK, and another control switch 58 that is normally closed when the vehicle service brakes are released. Solenoid 54 is not bi-stable and is spring biased to project armature 60 into another locking notch 62 in pushbutton 34.
As can be seen by FIG. 1, if all of switches 42, 56 and 58 are closed (ignition in RUN, shift lever in PARK, and brake released), solenoid 54 will be actuated to extend armature 60 to locking position, preventing movement of the shift lever out of PARK. However, if any of switches 42, 56 and 58 are open (i.e. ignition in OFF, or shift lever out of PARK, or brake applied), the circuit will be opened, deactuating solenoid 54, enabling spring retraction of armature 60. With the ignition in RUN, the brake must be applied to enable retraction of armature 60. This is the BTSI function.
Ignition switch 44 is open in OFF and ACCESSORY positions, while switch 42 is closed only in OFF position. The ignition/shifter interlock as shown in FIG. 1 is responding to a "low" input signal to controller 12, with the ignition key in OFF and the shifter lever in PARK. Insertion of the key and movement to RUN will close both switches 42 and 44, providing a "high" signal to controller 12 through switch 42. This retracts armature 30, freeing the shift lever for movement out of PARK only if the service brake is also applied to open switch 58 and retract armature 60.
It would be desirable to simplify this circuit, while providing both the BTSI and the ignition/transmission lever interlock functions.